Sensirion SHT11 with a PIC16F628-20

[gbm_designs]

Greetings-

I 've recently moved from the BS2 to the PIC Basic Compiler Pro software.


I'm trying to attach a Sensirion SHT11 Temperature and Humidity sensor to the Pic 16F628-20 and then send the Calculated values in Celcius and Farenheit, as well as Relative Humidity %RH to the COM1 port on my windows machine.

I have found many sample source code, but none seem to work for me when I compile. Either written for a separate compiler, or a different chip, so the #Include statements are wrong.

Can anyone help me along here? I would really appreciate it.

If any other information is required, please let me know.


Thank you,

Christian
EPIC PROGRAMMER
PIC BASIC COMPILER PRO
16F628-20
20-MHz External Xtal

[NavMicroSystems]

attached is a working piece of code for the 16F628



___________________

' Temperature, Relative Humidity and Dewpoint
' Processor : 16F628
' Sensor : SHT1x / SHT7x
' Display : 16x2

'** Pin-Assingments

dta VAR PORTB.1 ' Sensor Data
clk VAR PORTB.0 ' Sensor Clock

'** Constants

cmdtr CON %00000011 ' Command "read temperature"
cmdhr CON %00000101 ' Command "read humitity"

'** Variables

result VAR WORD ' RAW Data from Sensor
chksum VAR BYTE ' Checksum
cmd VAR WORD ' Sensor Command
RHlin VAR WORD ' Rel. Humidity (RH) Linear (% *10)
RHtc VAR WORD ' Rel. Humidity (RH) temp. compensated (% *10)
Temp VAR WORD ' Temperature (°C *100)
DP VAR WORD ' Dewpiont (°C *10)


'** Temp variables used in div. calculations

TempDP VAR WORD
Rchk VAR BYTE
logEW VAR WORD
sign VAR BIT
wy VAR WORD
wz VAR WORD
wj VAR WORD
wx VAR WORD
i VAR BYTE
ix VAR BYTE
bt VAR BIT


Pause 500
LCDOut $FE,1,"** SHT 11 **"
PAUSE 1000

main:

GoSub init
cmd = cmdtr

GoSub readsensor
Temp=result-3995

GoSub init
cmd = cmdhr

GoSub readsensor
RHlin=(26542-(54722**result+result))**result-40 ' RH linear
RHtc=655+(result*5)+(result**15917)
RHtc=(RHtc**(Temp/10+2480))-(RHtc**2730)+RHlin ' RH temp. compensated

GoSub dewpoint

LCDOut $FE,$80," ",$DF,"C"," ",$25,"RH"," DP "
LCDOut $FE,$C0,DEC2 (TEMP/100),".",DEC1 (temp/10)," ",DEC2 RHTC/10,".",DEC1 RHTC," ",DEC2 ABS DP/10,".",DEC1 ABS dp
sleep 10
GoTo main

'** Init Sensor
init:
High dta
Low clk
For i=1 to 10
High clk
Pause 1
Low clk
Pause 1
Next i
Call tstart
Return

'** start transfer
tstart:
High clk
Pause 1
Low dta
Pause 1
Low clk
Pause 1
High clk
Pause 1
High dta
Pause 1
Low clk
Return

'** get Data from Sensor
readsensor:
GoSub tstart
GoSub WaitSensor

ShiftOut dta,clk,1,[cmd\8] ' send command
Input dta ' wait acknowledge
Low clk
While dta=1
Wend
PulsOut clk,10 ' send ack
While dta=0
Wend
While dta=1 ' wait for conversion to complete
Wend
Low clk
ShiftIn dta,clk,0,[result.highbyte\8] ' get first byte
Low dta
PulsOut clk,10 ' send ack
ShiftIn dta,clk,0,[result.lowbyte\8] ' get second byte
Low dta
PulsOut clk,10 ' send ack
ShiftIn dta,clk,0,[chksum\8] ' get third byte (checksum)
High dta
PulsOut clk,10 ' send ack
Input dta ' End of Transmission
Input clk

Return

'** Dewpoint Calculation
' See: SENSIRION Application Note "Dewpoint Calculation"
' logEW = (0.66077+7.5*T/(237.3+T)+(log(RH)-2)
' DP = ((0.66077-logEW)*237.3)/(logEW-8.16077)

DewPoint:

TempDP=Temp/10
logEW=6608
sign=TempDP.bit15
wz=ABS TempDP
wx=(7*wz)+(wz/2)
wy=2373+wz
wj=wx/wy
For ix=15 to 0 step -1
wx=(wx//wy)<<1
wz.bit0(ix)=wx/wy
Next
wx=(-sign^((wj*10000)+(wz**10000)))+sign
logEW=wx+logEW
wx=RHtc
wj=(NCD wx) - 1
wx=wx<<(15-wj)
wz=0
For ix=14 to 0 step -1
wy=wx**wx
wz.bit0(ix)=wy.bit15
bt=~wy.bit15
wx=(wy<<bt)+(bt && wx.bit15)
Next

wx=((wj*4000)**49321)+(wz**6021)
logEW=wx+logEW-30000
sign=logEW.bit15
logEW=(-sign^(((ABS logEW)+2)/4))+sign
wx=1652-logEW
sign=~wx.bit15
wx=ABS wx
wy=20402-logEW
wj=wx/wy

For ix=15 to 0 step -1
wx=(wx//wy)<<1
wz.bit0(ix)=wx/wy
Next

DP=((23730**wz)+5)/10
DP=(-sign^DP)+sign

Return

WaitSensor:
result=4096
Loop:
result=result-1
IF dta && result.bit11 Then Loop
Return
End
___________________



Regards

Ralph

[gbm_designs]

Greetings Ralph-

Thank you for your help.

PROBLEMS:

PROBLEM1.
I get a COMPILE ERROR in this Section of Code:

DewPoint:

For ix=14 to 0 step -1
wy=wx**wx
wz.bit0(ix)=wy.bit15
bt=~wy.bit15
wx=(wy< Next <<<<---------THIS IS THE PROBLEM


QUESTION: Can you let me know what's missing here?

************************
PROBLEM2:
After COMMENTING out the ERROR LINE is PROB1, I set up the circuit as described below ((SEE CIRCUIT SPECS)) and use Hyperterminal to view the Output of the Program by COMMENTING out the LCD output in your code and replacing it with the following:

SerOut2 PORTB.2,86,[DEC2 (TEMP/100),".",DEC1 (temp/10)," ",DEC2 (TEMP/100),".",DEC1 (temp/10)," ",DEC2 RHTC/10,".",DEC1 RHTC," ",DEC2 ABS DP/10,".",DEC1 ABS dp,13,10]
'LCDOut $FE,$C0,DEC2 (TEMP/100),".",DEC1 (temp/10)," ",DEC2 RHTC/10,".",DEC1 RHTC," ",DEC2 ABS DP/10,".",DEC1 ABS dp


WHAT HAPPENS: I get the SAME Values over and over again

** SHT 11 **
12.8 00.4 12.3
12.8 12.8 00.4 12.3

QUESTION: ANY IDEAS?

************************

CIRCUIT SPECS:

PIC16F628-20
PINOUTS
4-----MCLR---4.7kohm to 5vdc
5-----VSS-----GND
6-----RB0-----Pin3 of SHT11 (SCK)
7-----RB1-----Pin2 of SHT11 (Data)
8-----RB2-----Pin10 of MAX232 (T2IN)
15---OSC2---XTAL (4Mhz)
16---OSC1---XTAL (4Mhz)


SHT11
PINOUTS
1----GND----GND
2----DATA---Pin7 of PIC (RB1)
3----SCK --- Pin6 of PIC (RB0)
4----VDD----5VDC


THANKS,

I hope this description is complete enough

CHRISTIAN

[NavMicroSystems]

Christian,

initially I tried to post the example using " [ code ] ... [ /code ] "

when I viewed my posting I had to realize the code was truncated at some point.

I have edited my posting and the full code is now there as plain ASCII.

please reload the code.

regards

Ralph

[gbm_designs]

Greetings Ralph-

It appears that the source code is the same.

I did a quick line comparison and the same number of characters are present.

Could you e-mail it to me?

Thank you

mailto: [email protected]


Christian

[NavMicroSystems]

. . .Could you e-mail it to me?



DONE!

[gbm_designs]

Greetings Ralph-

Thank you for the E-mail.

I used the new code with my changes for the Serial Port, rather than LCD.

However I still get the same value over and over.

** SHT 11 **
RH DP •
12.8 12.8 00.4 14.9


RH DP •
12.8 12.8 00.4 14.9


Kind of odd.


I re-tested this SHT11 Device with my BS2 Program and hardware and it works fine.

I have GOT to be doing something WRONG.



Christian

[NavMicroSystems]

Christian,

I'll have a look at it tomorrow morning when I'm back at my desk.

regards

Ralph

[gbm_designs]

I'll keep banging away at it tonight also.



I'll let you know what I find.


Christian

[Original]

Look at this:


'*******************************[ SHT11 Sample Code ]********************************
' File...... SHT11.bas
' Purpose... SHT11 digital humidity sensor sample code
' MCU....... Microchip PIC16F877
' Software.. Converted to Proton+ 2.0 from PBPro ver 2.4
' Author.... Brandon Tarr
' E-Mail.... [email protected]
' Web....... http://www.spectrumedix.com
' Started... May 15, 2002
' Updated...
' Version... 1.0
'************************************************* *************************

device 16f877

DEFINE xtal 4
Define LCD_DREG PORTD
Define LCD_DBIT 4
Define LCD_RSREG PORTE
Define LCD_RSBIT 0
Define LCD_EREG PORTE
Define LCD_EBIT 1

TEMP con 1
HUMI con 2
' adr command r/w
Symbol statusregw = $06 ' 000 0011 0
Symbol statusregr = $07 ' 000 0011 1
Symbol measuretemp = $03 ' 000 0001 1
Symbol measurehumi = $05 ' 000 0010 1
Symbol resett = $1e ' 000 1111 0

' -----[ Variables ]---------------------------------------------------------------------
Dim SCK as PORTC.3 ' SHT11 SCK
Dim SDATA as PORTC.4 ' SHT11 DATA

Dim i as byte
Dim f as byte
Dim value as byte
Dim errorr as bit
Dim mode as byte
Dim ack as bit

Dim vall as byte
Dim pktvalue as word
Dim pktchksum as byte

Dim humival as word
Dim tempval as word
Dim dewpoint as byte
Dim checksum as byte

' -----[ Initialization ]----------------------------------------------------------------
ADCON1 = 7 ' Set PORTA and PORTE to digital
Low PORTE.2 ' LCD R/W line low (W)
Pause 100 ' Wait for LCD to start
lcdout $fe, 1

' -----[ Main Code ]---------------------------------------------------------------------
usetheSHT11:
gosub connectionreset
value = measurehumi
gosub measure ' measure humidity
humival = pktvalue * 1000
humival = DIV32 4095
lcdout $fe, 2, " ", $fe, 2, "Humidity: ", dec humival / 10, ".", dec humival // 10, "%"
value = measuretemp
gosub measure ' measure temperature
tempval = pktvalue * 1000
tempval = DIV32 16383
lcdout $fe, $c0, " ", $fe, $c0, "Temperature: ", dec tempval / 10, ".", dec tempval // 10, 223, "C"
pause 100 ' decrease sample time
goto usetheSHT11

' -----[ Subroutines ]-------------------------------------------------------------------
connectionreset:
' communication reset: DATA line is high and at least 9 SCK cycles followed by transstart
' ________________________________________ _____
' SDATA: |_____|
' _ _ _ _ _ _ _ _ _ __ __
' SCK: _| |_| |_| |_| |_| |_| |_| |_| |_| |___| |__| |___
high SDATA
low SCK ' set initial state
for i = 1 to 9 ' 9 SCK cycles
high SCK
low SCK
next
gosub transstart ' transmission start
return

transstart:
' generates a transmission start
' ___ _____
' SDATA: |_____|
' __ __
' SCK: __| |__| |___

high SDATA
low SCK ' set initial state
high SCK
low SDATA
low SCK
high SCK
high SDATA
low SCK
return

measure:
' makes a measurement (humidity/temperature) with checksum
errorr = 0
gosub transstart ' transmission start
gosub writebyte
for i = 1 to 255 ' wait until sensor has finished the measurement
if SDATA = 0 then
goto meascomplete
endif
pause 1
next
meascomplete:
if SDATA != 0 then ' or timeout (~2 sec.) is reached
errorr = 1
endif
ack = 1
gosub readbyte ' read the first byte (MSB)
pktvalue.highbyte = vall
gosub readbyte ' read the second byte (LSB)
pktvalue.lowbyte = vall
ack = 0
gosub readbyte ' read checksum (no acknowledge to put sensor in "sleep" mode)
pktchksum = vall
return

writebyte:
' writes a byte on the Sensibus and checks the acknowledge
errorr = 0
i = $80
while i > 0
if (i & value) != 0 then ' masking value with i
high SDATA ' write to SENSI-BUS
else
low SDATA
endif
high SCK ' clk for SENSI-BUS
low SCK
i = i / 2 ' shift bit for masking
wend
high SDATA
TRISC.4 = 1 ' release SDATA-line
high SCK ' clk #9 for ack
errorr = SDATA ' check ack (SDATA will be pulled down by SHTXX)
low SCK
return

readbyte:
' reads a byte from the Sensibus and gives an acknowledge in case of "ack=1"
vall = 0
high SDATA
TRISC.4 = 1 ' release SDATA-line
i = $80
while i > 0
high SCK ' clk for SENSI-BUS
if SDATA = 1 then ' read bit
vall = vall | i
endif
low SCK
i = i / 2
wend
TRISC.4 = 0 ' grab SDATA-line
SDATA = ack ' in case of "ack", pull down DATA-Line
high SCK ' clk #9 for ack
low SCK
high SDATA
TRISC.4 = 1 ' release SDATA-line
return

softreset:
' resets the sensor by a softreset
errorr = 0
GOSUB connectionreset ' reset communication
value = resett
gosub writebyte ' send RESET-command to sensor
return

[cibotsan]

hi! iam also working SHT11 project with PIC16F877 display with LCD, itry Ralph source code but, only **SHT 11** display no sensor reading ,can someone email source code to me? [email protected]
thanks

[ronf]

For anyone trying to get this first off, add wx=wy<< bt+(bt & wx.bit15)
instead of the truncated part Christian had indicated.
(nice work on the code Ralph)
This works fine on a PIC16F876A 20mhz using portc.3 and portc.4
I can see why Ralph had problems with it not posting properly. I had to
put in a space before the first bt to see it properly as without the space
it was truncating my reply too. Anyone else have a problem posting code
like this?
(helps to look at the preview)
Hope this helps someone.
Ron

[Evolution]

I have been trying to get this code to work for the last week,A friend and i have both recived samples and have been unable to get the project going after overcoming the first compile error it seems that the device wont respond and it just hangs in the readsensor routine, Could yoiu please post the working picbasic pro or email it to me at [email protected].
it seems that if i force data line to go low by shorting to ground the code execution continues and outputs repative numbers.
There is a misplaced next could you please clarafy where this is ment to go

regards Evolution

[Acetronics2]

just see that ...

http://www.parallax.com/dl/src/prod/shtdocscode.zip

Alain

[Evolution]

Why bother running the forum im sure all of us have no worries translating the cryptic data presented in these sheets and great bs2 code????? pbp

[Acetronics2]

Why bother running the forum im sure all of us have no worries translating the cryptic data presented in these sheets and great bs2 code????? pbp

Hi,

Sorry ... but could you be more explicit ... difficulties to fully understand your answer.

Alain

[Evolution]

First of all i had the code error where the example was missing (wx=(wy< Next <<<<---------) after replacing this with the example above it seems that code execution halts on waiting for initalisation command(data pulled low) and nothing will happen untill i manualy ground the pin temproraly oncei do this it outputs repeating numbers in an unordly fashion
i am using picbasic pro 2.44 but can also code in assembly the selected mcu is a pic16f628 a running at 4mhz internal osc
Would greatly appreciate any help you could provide i had a look at the bs2 code you pointed out and will try to convert it to picbasic

[adamchapman]

I'm using the above code with a 16f84a and getting a consistent number, which is clearly wrong. I'm getting humvalue 16003 and tempval 4000. And since I haven't burst into flames this seems unlikely to be accurate.

I also tried using a modified Keunyoung Oh's code for the 16f877 (found http://itp.nyu.edu/physcomp/sensors/Code/SHT11 ) but received similar results (consistent & wildly inaccurate numbers), though with different numbers.

Any idea why this might be?

Also, as a possible explanation: I'm using the DIP sht11 which has a 117 on the sensor. I'm assuming I should use the pin diagram which goes with sensirion sht11 sensor module #28018, but all the other pin diagrams are different.

any suggestions would be helpful.

thanks,
Adam

[adamchapman]

here's the full code I'm currently (trying to use) everything compiles and publishes in PBP, but still no good data. is my code messed up?


'*******************************[ SHT11 Sample Code ]********************************
' File...... SHT11.bas
' Purpose... SHT11 digital humidity sensor sample code
' MCU....... Microchip PIC16F877
' Software.. Converted to Proton+ 2.0 from PBPro ver 2.4
' Author.... Brandon Tarr
' E-Mail.... [email protected]
' Web....... http://www.spectrumedix.com
' Started... May 15, 2002
' Updated...
' Version... 1.0
'************************************************* *************************

'device 16f884a

DEFINE xtal 4
Define LCD_DREG PORTD
Define LCD_DBIT 4
Define LCD_RSREG PORTE
Define LCD_RSBIT 0
Define LCD_EREG PORTE
Define LCD_EBIT 1

TEMP con 1
HUMI con 2
' adr command r/w
Symbol statusregw = $06 ' 000 0011 0
Symbol statusregr = $07 ' 000 0011 1
Symbol measuretemp = $03 ' 000 0001 1
Symbol measurehumi = $05 ' 000 0010 1
Symbol resett = $1e ' 000 1111 0

' -----[ Variables ]---------------------------------------------------------------------
ledPin var PORTB.0
ledVar var byte

rxPin var PORTB.3
txPin var PORTB.2
SCK var PORTA.4 ' SHT11 SCK
SDATA var PORTB.1 ' SHT11 DATA

i var byte
f var byte
value var byte
errorr var bit
mode var byte
ack var bit

vall var byte
pktvalue var word
pktchksum var byte

humival var word
tempval var word
dewpoint var byte
checksum var byte

' -----[ Initialization ]----------------------------------------------------------------
'ADCON1 = 7 ' Set PORTA and PORTE to digital
'Low PORTE.2 ' LCD R/W line low (W)
Pause 500 ' Wait for LCD to start
'lcdout $fe, 1

' -----[ Main Code ]---------------------------------------------------------------------
usetheSHT11:
SerOut2 txPin, 16468, [" ", 10, 13]
High ledPin ' Turn on LED connected to PORTB.0
Pause 500 ' Delay for .5 seconds
Low ledPin ' Turn off LED connected to PORTB.0

gosub connectionreset
value = measurehumi
gosub measure ' measure humidity
humival = pktvalue * 1000
humival = DIV32 4095
'lcdout $fe, 2, " ", $fe, 2, "Humidity: ", dec humival / 10, ".", dec humival // 10, "%"
value = measuretemp
gosub measure ' measure temperature
tempval = pktvalue * 1000
tempval = DIV32 16383
'lcdout $fe, $c0, " ", $fe, $c0, "Temperature: ", dec tempval / 10, ".", dec tempval // 10, 223, "C"
SerOut2 txPin, 16468, ["humival ", DEC humival, 10, 13]
SerOut2 txPin, 16468, ["tempval ", DEC tempval, 10, 13]

pause 500 '100 decrease sample time
goto usetheSHT11

' -----[ Subroutines ]-------------------------------------------------------------------
connectionreset:
' communication reset: DATA line is high and at least 9 SCK cycles followed by transstart
' ________________________________________ _____
' SDATA: |_____|
' _ _ _ _ _ _ _ _ _ __ __
' SCK: _| |_| |_| |_| |_| |_| |_| |_| |_| |___| |__| |___
input SDATA
high SDATA
low SCK ' set initial state
for i = 1 to 9 ' 9 SCK cycles
high SCK
low SCK
next
gosub transstart ' transmission start
return

transstart:
' generates a transmission start
' ___ _____
' SDATA: |_____|
' __ __
' SCK: __| |__| |___

high SDATA
low SCK ' set initial state
high SCK
low SDATA
low SCK
high SCK
high SDATA
low SCK
return

measure:
' makes a measurement (humidity/temperature) with checksum
errorr = 0
gosub transstart ' transmission start
gosub writebyte
for i = 1 to 255 ' wait until sensor has finished the measurement
if SDATA = 0 then
goto meascomplete
endif
pause 1
next
meascomplete:
if SDATA != 0 then ' or timeout (~2 sec.) is reached
errorr = 1
endif
ack = 1
gosub readbyte ' read the first byte (MSB)
pktvalue.highbyte = vall
gosub readbyte ' read the second byte (LSB)
pktvalue.lowbyte = vall
ack = 0
gosub readbyte ' read checksum (no acknowledge to put sensor in "sleep" mode)
pktchksum = vall
return

writebyte:
' writes a byte on the Sensibus and checks the acknowledge
errorr = 0
i = $80
while i > 0
if (i & value) != 0 then ' masking value with i
high SDATA ' write to SENSI-BUS
else
low SDATA
endif
high SCK ' clk for SENSI-BUS
low SCK
i = i / 2 ' shift bit for masking
wend
high SDATA
TRISB.1 = 1 ' release SDATA-line
high SCK ' clk #9 for ack
errorr = SDATA ' check ack (SDATA will be pulled down by SHTXX)
low SCK
return

readbyte:
' reads a byte from the Sensibus and gives an acknowledge in case of "ack=1"
vall = 0
high SDATA
TRISB.1 = 1 ' release SDATA-line
i = $80
while i > 0
high SCK ' clk for SENSI-BUS
if SDATA = 1 then ' read bit
vall = vall | i
endif
low SCK
i = i / 2
wend
TRISB.1 = 0 ' grab SDATA-line
SDATA = ack ' in case of "ack", pull down DATA-Line
high SCK ' clk #9 for ack
low SCK
high SDATA
TRISB.1 = 1 ' release SDATA-line
return

softreset:
' resets the sensor by a softreset
errorr = 0
GOSUB connectionreset ' reset communication
value = resett
gosub writebyte ' send RESET-command to sensor
return

[tonyfelloni]

Hmmmm. This was a valid interesting topic.... pity it ends in the middle of nowhere without a solution!

[skimask]

Hmmmm. This was a valid interesting topic.... pity it ends in the middle of nowhere without a solution!

I think there are a couple of other working examples somewhere here on the forums.
And heck, if the original poster doesn't care if the problem is solved, why should anyone else?

[tonyfelloni]

Hey Skimask

I care because its relevant to something I am working on now.... To find the perfect thread....only to discover you have been led up the garden path, haha. Not to worry, I did see a few other relevant posts elsewhere.

Cheers
Tony

[psenek]

Hi!

I know this is an old thread but this might still help someone.

NavMicroSystems' example works fine, if you place wx=wy<< bt+(bt & wx.bit15)
instead of wx=(wy< Next.

It has some issues with negative temperatures but ok...

It's important that you don't forget 10k pullup on DTA line.

There's one more thing: you should replace all HIGH dta
commands with INPUT dta.

Datahseet SHT1x @ page 5.

"To avoid signall contention the microcontroller must only
drive DATA low".

When you have appropriate (10k) pullup on dta the line
goes high if you set the dta pin to input. I tested it and
it works perfectly fine.

Also: if this is your first attempt to communicate with SHT1x maybe
you should consider omitting dewpoint calculations and just read
raw data.

For room ambient (i had about 22°C and 35 %RH when testing) you should
get readings like 0x1855 for 14bit temperature and 0x03EE for 12bit humidity).

Best regards,

Rok

[yohanfx]

I want to program SHT11, with language PBP or Pbasic
want to know the temperature and humidity with SHT11.
please help me ....

[Charles Linquis]

I have successfully used the code below with an 18F2321.
It should work the same with a 16F part.

I found it somewhere here on the forum, and it works great.




'------------------ Read SHT71 Temperature / Humidity Sensor -------------------

ReadSHT71:
SHTCommand = ReadTemp
gosub Initialize
GOSUB TransmissionStart
GOSUB IssueCMD
gosub ConvertToCelsius


SHTCommand = ReadHumidity
gosub Initialize
GOSUB TransmissionStart
GOSUB IssueCmd
gosub ConvertToRH

TEMPC = (TempC/100) - 2
TempC.7 = SignC
RHTempComp = RHTempComp/100
RETURN



'--------------------- Calculate Relative Humidity -----------------------------

ConvertToRH:
' 12 Bit RHLinear = -4 + 0.0405 * DataOutput -0.0000028 * DataOutput^2
w = 405 * RawData
w = div32 100
x = RawData * RawData
x = div32 1000
x = x * 28
x = div32 100
RHLinear = w - x - 400

'---------- Calculate Relative Humidity with Temperature Compensation ----------

w = (8 * RawData + 1000) / 10
IF SignC = 0 THEN ' "+"
if tempC > 2500 then
x = (tempC - 2500) * w
x = div32 100
RHTempComp = RHLinear + x / 100
else
x = (2500 - tempc) * w
x = div32 100
RHTempComp = RHLinear - x / 100
endif
else
x = (2500 + tempC) * w
x = div32 10000
RHTempComp = RHLinear - x
endif
return

'---------------------------- Initialize the Sensor ----------------------------

Initialize:
high DataPin ; Start condition
low clk
for i = 1 to 10
high clk
pause 1
low clk
pause 1
next i ; Leaves clock low

return

'---------------------------- Get Data from Sensor -----------------------------

IssueCmd:
Pause 2
low Clk
shiftout DataPin,clk,1,[SHTCommand\8] ' Send command byte
input DataPin

WaitForAck:
x = 0
WaitForAck2:
IF DataPin = 1 THEN
x = x + 1
if x = 0 then goto NoAck
Pauseus 2
GotoWaitForAck2
ENDIF

High Clk
pause 10 ' Issue ACK from PIC
low clk

pause 10 ' Make certain we don't move forward on a glitch

WHILE DataPin:WEND


shiftin DataPin,clk,0,[RawData.byte1\8] ' Get the first byte, 8 bits
low DataPin

HIGH Clk
PAUSE 10
LOW Clk
pulsout clk,10 ' Send NACK
shiftin DataPin,clk,0,[RawData.byte0\8] ' Get the second byte, 8 bits


low DataPin
pulsout clk,10 ' Send acknowledge
shiftin DataPin,clk,0,[crc\8] ' Get third byte, 8 bits, CRC
high DataPin
pulsout clk,10 ' Send acknowledge
input DataPin ' End of Transmission
input clk

ERR = 0
return

NoAck:
ERR = 1
RETURN

'---------------------------- Start Transfer -----------------------------------

TransmissionStart:
HIGH DataPin ; Make sure it is high
Pause 1
high clk
pause 1
low DataPin
pause 1
low clk
pause 1
high clk
pause 1
high DataPin
pause 1
low clk
return

'----------------------------- Raw Data to Degrees C ---------------------------


ConvertToCelsius:
' 14 Bit Temperature = -40.00 + 0.01 * DataOutout
if RawData => 4000 then
tempC = RawData - 4000
SignC = 0

else
tempC = 4000 - RawData ; Negative Temps
SignC = 1

endif
return

[yohanfx]

what software you use as a compiler?
pardon my beginner programing and
program how to display the sensor readings of temperature and humidity SHT11 to 16bit and two-line LCD ....
thanks very much

[iw2fvo]

Hi ,
I am going to implemant the dew point computation with this sensor and with a PIC badìsic Pro.
I agree that there is an errot in DP calculation when the temperature is under 0°C.
Any help to solve the problem? Or any updated code ?
Thanks for helping.
Regards,
Ambrogio




Hi!

I know this is an old thread but this might still help someone.

NavMicroSystems' example works fine, if you place wx=wy<< bt+(bt & wx.bit15)
instead of wx=(wy< Next.

It has some issues with negative temperatures but ok...

It's important that you don't forget 10k pullup on DTA line.

There's one more thing: you should replace all HIGH dta
commands with INPUT dta.

Datahseet SHT1x @ page 5.

"To avoid signall contention the microcontroller must only
drive DATA low".

When you have appropriate (10k) pullup on dta the line
goes high if you set the dta pin to input. I tested it and
it works perfectly fine.

Also: if this is your first attempt to communicate with SHT1x maybe
you should consider omitting dewpoint calculations and just read
raw data.

For room ambient (i had about 22°C and 35 %RH when testing) you should
get readings like 0x1855 for 14bit temperature and 0x03EE for 12bit humidity).

Best regards,

Rok